Portland State University PDXScholar Dissertations and Theses Dissertations and Theses Spring 6-8-2017 Ecosystem Recovery in Estuarine Wetlands of the Columbia River Estuary Sarah Ann Kidd Portland State University Follow this and additional works at: https://pdxscholar.library.pdx.edu/open_access_etds Part of the Natural Resources and Conservation Commons, and the Plant Sciences Commons Let us know how access to this document benefits ou.y Recommended Citation Kidd, Sarah Ann, "Ecosystem Recovery in Estuarine Wetlands of the Columbia River Estuary" (2017). Dissertations and Theses. Paper 3637. https://doi.org/10.15760/etd.5521 This Dissertation is brought to you for free and open access. It has been accepted for inclusion in Dissertations and Theses by an authorized administrator of PDXScholar. Please contact us if we can make this document more accessible: [email protected]. Ecosystem Recovery in Estuarine Wetlands of the Columbia River Estuary by Sarah Ann Kidd A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Sciences and Resources Dissertation Committee: Alan Yeakley, Chair Martin Lafrenz Jennifer Morse Yangdong Pan Sarah Eppley Portland State University 2017 © 2017 Sarah Ann Kidd Abstract In the restoration of tidal wetland ecosystems, potential drivers of plant community development range from biotic controls (e.g. plant competition, seed dispersal) to abiotic controls (e.g. tidal flooding, salinity levels). How these controls influence the success of tidal wetland restoration are only partly understood, but have important implications for wetland habitat recovery. Specifically, the extent to which the existing native and non-native seed banks in tidally reconnected wetlands interact with these controls is not clear, yet the potential success of passive restoration methods depends upon this understanding. For a 54-year chronosequence of eleven tidal wetland restoration sites in the Lower Columbia River of western Oregon, USA, it was hypothesized that native plant species and soil properties would show trends approaching reference levels within 3 to 20 years post-restoration and that lower elevation wetland areas within restored sites would exhibit a greater native species abundance and similarity to reference sites, compared with restored high elevation wetland areas. Results indicated that plant species richness, soil organic matter, bulk density, pH, and salinity conditions among the restoration sites reached reference wetland ranges within 3-6 years post-tidal reconnection. The mid-low marsh elevation zones (<2.5 m) recovered native plant cover within 3-6 years post-tidal reconnection, while high marsh elevation zones (>2.5 m) remained dominated by non- native species Phalaris arundinacea and Juncus effusus subsp. effusus. To investigate the mechanisms driving these non-native plant invasions, it was i hypothesized that native and non-native wetland plant community distributions would be reflective both of their abundance in the seed bank and of their germination tolerance to wetland tidal flooding and salinity conditions. Using a factorial study design of three tidal conditions by three salinity levels, these hypotheses were tested in the greenhouse. Overall, non-native seeds were found to significantly outnumber native seeds in both seed banks. In the greenhouse, P. arundinacea and J. effusus were found to germinate more readily out of the seed bank under freshwater high-marsh flooding (1 hour a day) treatments as compared to oligohaline (3 ppt) mid-low marsh flooding (3-6 hours twice a day) treatments and to brackish salinity (10 ppt) treatments. Dominant native wetland species, Carex lyngbyei and Schoenoplectus lacustris, germination were not found to vary significantly among the treatments (p > 0.10). These results indicate that the salinity and flooding gradients within these restored marshes suppress germination of the non-native species in the low-mid marsh but not in the high marsh, where they are likely able to outcompete the native species due to their dominance in the seed bank. The implications of these results for passive tidal wetland restoration efforts are that both seed bank composition and species-specific tolerances to restored tidal flooding and salinity gradients are key mechanisms driving native and non- native plant community development and resilience. ii Acknowledgements I would like to acknowledge and thank my advisor Alan Yeakley, without his support, continued guidance, expertise, and encouragement this dissertation would not have been possible. I would also like to thank my dissertation committee members Martin Lafrenz, Jennifer Morse, Yangdong Pan, and Sarah Eppley for their continued guidance, insight, and support throughout the dissertation research and writing process. I have truly enjoyed being their student and am grateful for their support. I would like to thank the National Science Foundation IGERT and GK12 fellowship programs for providing me the resources and support necessary to conduct this research. I would especially like to thank Kim Heavener, Dave Ervin, Darrell Brown, Elise Granek, Heejun Chang, Patrick Edwards, Catherine de Rivera, Linda George, and Sherie Huffman for providing me with outstanding education opportunities and support through these NSF fellowships. I am also very grateful for the additional grant funding and support I received from The National Parks Service North Coast and Cascades Science Learning Network, The Northwest Scientific Association, Portland State University Institute for Sustainable Solutions, The Society for Ecological Restoration, and The Society of Wetland Scientists. I am very thankful to the Lewis and Clark National Historical Park, the Cowlitz Tribe of Washington, the Columbia Land Trust, the Port of Astoria, and the City of Seaside for providing access to all of the restoration sites, without access to these sites my research would not have been possible! I would like to especially recognize the ongoing support and encouragement from the Lewis and Clark National Historical Park iii staff, Carla Cole and Christopher Clatterbuck, and Rudy Salakory with the Cowlitz Tribe of Washington. The Lower Columbia River Estuary Partnership and the Columbia River Estuary Study Taskforce also proved resources and information essential to these research efforts. I would like to recognize the invaluable help I received from all of my lab and close schoolmates: Josh Caplan, Denisse Fisher, Christa von Behren, Ted Hart, Gunnar Johnson, Kate Norton, Nicole Alfafara, Brian Turner, Ben Shetterly, Sheree Watson, and my IGERT cohort: Marissa Matsler, Paul Mason, Jodi Schoenen, Roy Watters, Basma Mohammad, Erin Goodling, and Jamal Green who provided endless amounts of help, moral support, and advice during this six year journey. I would like to thank my research assistants, interns, and friends including but not limited to: Katrina Dunn, Drew Mahedy, Luke Murphy, Juan Rueda Callejas, Meredith Condon, Ann Stahl, Jazzmine Allen, Nathan Kossnar, Jonathan Hawkes, Michelle Majeski, Eve Jakabosky, Hillary Picha, Amelia Fitch, Benjamin Burton, Jacob Argueta, Steven Witt, William Cheek, and Kim Biafora who spent many hours in the beating sun, pouring rain, mud, cow patties, in the soils lab, and/or in a sweltering greenhouse helping me collect and process all of my data over the last six years. Without their help, friendship, and enthusiasm I would surely never have survived my data collection. I am also endlessly grateful to my mom and dad, Dan and Trudy Holmen, who have not only supported and encouraged me in my educational pursuits my entire life but also took time off work to helped me collect data and to build equipment for the greenhouse! Lastly, I owe a huge thank you to my wonderful husband, Brian Kidd, who spent countless hours and late iv nights helping me with data collection, entry, editing and providing endless amounts of encouragement. v Table of Contents Abstract ................................................................................................................................ i Acknowledgements ............................................................................................................ iii List of Tables ..................................................................................................................... xi List of Figures .................................................................................................................. xiv 1 Chapter 1: Introduction to Restoration of Tidal Wetlands in the Columbia River Estuary .................................................................................................................................1 1.1 Research Context...................................................................................................1 1.2 Columbia River Estuary ........................................................................................3 1.2.1 Geography: Tides, Salinity ............................................................................3 1.2.2 Geography: Oligohaline Wetlands and Sea level Rise ..................................5 1.2.3 Drivers of Restoration: Dikes, Dams, and Salmon ........................................7 1.3 Tidal Wetlands: Restoration and Science..............................................................9 1.3.1 What is Restoration? ......................................................................................9 1.3.2 Theory of Ecological